(Bloomberg) -- Microsoft Corp. President Brad Smith warned the danger of foreign interference in the US election will surge in the final two days of the presidential campaign.

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“The most perilous moment will come, I think, 48 hours before the election,” Smith told the Senate Intelligence Committee on Wednesday.

Smith said that was the “lesson to be learned” from the Slovakian election last fall, in which fake audio of one of the top candidates circulated online days before the election.

Foreign actors already have been spreading manipulated videos and false posts to sow discord around the US presidential election, Smith and other executives with the country’s largest tech companies testified.

Smith said Microsoft earlier Wednesday had identified an “AI-enhanced” video from a Russian group showing Vice President Kamala Harris saying words she didn’t say at a recent rally.

Groups from adversarial nations including Russia, China and Iran have spread false information and news reports about both Harris and Donald Trump’s campaigns, the executives said.

The hearing featured testimony from Smith, Google parent Alphabet Inc.’s president and chief legal officer Kent Walker, and Nick Clegg, Meta Platforms Inc.’s president of global affairs.

Those attacks are being shaped in part by new developments in artificial intelligence, Walker said.

“We are seeing some foreign state actors experimenting with generative AI to improve existing cyber attacks, like probing for vulnerabilities or creating spear phishing emails,” Walker said. “We see generative AI being used to more efficiently create fake websites, misleading news articles and robot social media posts.”

The Senate Intelligence Committee hearing, focused on foreign interference in US elections, comes on the heels of a Microsoft report that found Russian efforts to influence the US election have shifted to smearing Harris with doctored and misleading videos. Meta on Tuesday also announced it was banning Russian state media outlet Russia Today due to “foreign interference.”

The Biden administration and the top tech companies stopped communicating about online threats to US elections over the past year as they waited for a ruling in Murthy v. Missouri, a case centered on whether it is constitutional for government officials to ask social media companies to take down certain posts.